5-Hydroxyindoleacetic acid

5-Hydroxyindoleacetic acid (5-HIAA) is a metabolite of the neurotransmitter serotonin. It is often measured in the urine of patients suspected of having carcinoid syndrome, a group of symptoms associated with carcinoid tumors which secrete large amounts of serotonin into the bloodstream.

Chemistry

5-HIAA is the main metabolite of serotonin, a biogenic amine found in the human body. Serotonin is metabolized by the enzyme monoamine oxidase to produce 5-HIAA, which is then excreted in the urine.

Clinical significance

In medicine, the level of 5-HIAA in the urine is used as a marker for the presence of carcinoid tumors. These tumors, which can occur in the gastrointestinal tract, lungs, and other parts of the body, secrete large amounts of serotonin. This leads to an increase in the level of 5-HIAA in the urine.

Measurement

The measurement of 5-HIAA levels is usually performed using a 24-hour urine collection. The patient is instructed to collect all urine produced over a 24-hour period, which is then analyzed in a laboratory. The level of 5-HIAA is usually reported in milligrams per 24 hours.

Interpretation

A high level of 5-HIAA in the urine is suggestive of a carcinoid tumor. However, other conditions can also cause an increase in 5-HIAA levels, including certain foods and medications, and stress. Therefore, the results of a 5-HIAA test must be interpreted in the context of the patient's overall clinical picture.

See also

• Serotonin
• Carcinoid syndrome
• Monoamine oxidase

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